On the main irradiation-induced defect in GaN

Abstract

We show that the usual Arrhenius analysis of the main electron-irradiation-induced defect trap in n-type GaN, observed by deep-level transient spectroscopy (DLTS), is not sufficiently accurate. Instead, an exact fitting of the DLTS spectrum for this trap reveals two components, each of which has a thermal energy near 60 meV, not the apparent 140–200 meV, as given in other DLTS studies. This result resolves the discrepancy between Hall-effect and DLTS determinations of the thermal energy of this defect center.

Plasma-etching-enhanced deep centers in n-GaN grown by metalorganic chemical-vapor deposition

“…Carrier concentrations in the control and plasma-etched samples, determined by C -V measurements on several SBDs for each sample, are somewhat nonuniform and can be classified into two groups: higher n (ϳ5ϫ10 16 cm Ϫ3 ) in group I, and lower n (ϳ2ϫ10 16 cm Ϫ3 ) in group II. All comparisons, presented subsequently, are made among samples in the same group, since similar trends in plasma-etchinginduced changes can be found for samples in a given group.…”

“…13 We can summarize our major results as follows: ͑i͒ trap D and the other traps are bulk-like in the unetched sample; ͑ii͒ trap D is greatly enhanced by plasma-etching at high bias-voltages, but the additional trap-D concentration is closer to the surface; ͑iii͒ traps A 1 , C, and E 1 are also enhanced in the surface region; and ͑iv͒ all of these traps behave as dislocation-related line defects. From previous studies, 5,16 we have shown that: ͑i͒ two DLTS centers, E ͑0.18 eV͒ and A 2 ͑0.90 eV͒ can be induced in MOCVD GaN by 1-MeV electron irradiation ͑EI͒; and ͑ii͒ the E center, which actually consists of two components ͑ED1 and ED2͒, is related the nitrogen vacancy (V N ), and the A 2 center might be related to the nitrogen interstitial (N I ). In the present study, four deep centers, A 1 ͑similar to A 2 ), C, D, and E 1 ͑similar to E͒, are significantly enhanced in the surface region of unintentionally-doped MOCVD GaN following ICP-RIE under high etching bias.…”

Radiation-induced defects in GaN bulk grown by halide vapor phase epitaxy

“…5,7,9 Fang et al 5 suggested the level to be related to the N vacancy (V N ). From simulation, this peak is suggested to consist of several overlapping levels.…”

“…[4][5][6][7][8][9] Fang et al found a deep defect level at 0.18 eV below the conduction band in electron-irradiated GaN, but its origin has not conclusively been identified. 5 Polenta et al 9 did a detailed study of electron irradiated metalorganic chemical vapor deposition (MOCVD) grown n-type GaN Schottky diodes in the temperature range of 80-400 K, revealing two severely overlapped DLTS peaks with the thermal activation energies of E C -0.06 eV and E C -0.11 eV, respectively. Another observation by Goodman et al suggested that there are at least three defects whose DLTS spectra overlapped with each other to form a broad peak with different activation energies (0.06 eV, 0.10 eV, 0.20 eV).…”

Thermoelectric effect spectroscopy of deep levels in semi-insulating GaN

“…22 However, detailed DLTS fitting shows that ͑i͒ E consists of ED1 and ED2; ͑ii͒ both centers have the same E T , 0.06 eV, which is very close to the 0.07 eV found for the EI-induced N-vacancy donor; and ͑iii͒ both centers have different and small capture cross sections ͑1 -3ϫ10 Ϫ20 cm 2 for ED1 and 5 -8ϫ10 Ϫ19 cm 2 for ED2), with that of ED2 being temperature dependent and having an activation energy (E ) of 0.06 eV. 23 We speculate that the hole trap (A 3 ) is due to the Ga vacancy, which is often the dominant acceptor in undoped GaN, especially that grown by hydride vapor phase epitaxy, as confirmed by positron annihilation studies. 24,25 According to theoretical calculations, 26 ͑i͒ the N vacancy ͑a donor͒ has the lowest formation energy in p-type GaN, and the Ga vacancy ͑an acceptor͒ in n-type GaN; and ͑ii͒ the isolated Ga vacancy in the negative charge state is triply occupied, with levels close to the valence band.…”